1. Field
Example embodiments relate to a resistance random access memory (RRAM) including a resistance layer having a metal oxide and/or a metal ion dopant and a method of manufacturing the same. The resistance layer of the RRAM may be formed at a lower temperature and may have better electrical characteristics, and thus an RRAM including the resistance layer may be more reliable and may be manufactured in a more cost-effective manner.
2. Description of Related Art
A semiconductor memory array includes many memory cells connected in a circuit. In a Dynamic Random Access Memory (DRAM), which is an example of a semiconductor memory device, a unit memory cell is composed of a switch and a capacitor. A DRAM is advantageous in that the DRAM has a higher degree of integration and operates at higher speeds. However, when the power supply to the DRAM is discontinued, all data stored in the DRAM is lost.
A flash memory device is an example of a nonvolatile memory device in which stored data is maintained even if the power supply is discontinued. However, although flash memory devices have nonvolatile characteristics unlike a volatile memory device, the degree of integration and operating speed thereof is less than those of a DRAM.
A vast amount of research has been conducted on nonvolatile memory devices (e.g., Magnetic Random Access Memory (MRAM), Ferroelectric Random Access Memory (FRAM), and Phase-change Random Access Memory (PRAM)).
In a MRAM, data is stored by changing the magnetization direction in the tunnel junction. In a FRAM, data is stored using polarization characteristics of ferroelectrics. Both MRAM and FRAM have advantages and disadvantages,
The PRAM includes a resistor and a switch (transistor), and stores data using the change in the resistance value caused by a phase change in a specific material. In a PRAM manufacturing process, an etching process cannot easily be performed when a conventional DRAM process is used. The etching process takes a longer time. Thus, the yield of the PRAM may decrease, and thereby, increase PRAM manufacturing costs.
The RRAM uses the variable resistance characteristics of a transition metal oxide in that the resistance value varies according to the applied voltage.
An example of a material that is used to form an RRAM is NiO. A NiO layer can have various current-voltage characteristics according to the deposition temperature.
The current-voltage characteristics of the NiO layer are illustrated in FIG. 1A.
In FIG. 1A, Sample 1 is a NiO layer deposited at room temperature using a sputtering method, and Sample 2 is a NiO layer deposited at a temperature of about 350° C. using a sputtering method. According to the current-voltage characteristics of Sample 1 that is deposited at room temperature, Sample 1 does not have variable resistance characteristics. On the other hand, according to the current-voltage characteristics of Sample 2 that is deposited at a temperature of about 350° C., Sample 2 has variable resistance characteristics. These results can be observed in FIG. 1B, which illustrates variable resistance characteristics of Sample 2 for a voltage in the range of 0.0-2.0 V.
Because Sample 1 is deposited at a lower temperature, Sample 1 does not have variable resistance characteristics, and thus Sample 1 cannot be used as an RRAM. However, a lower temperature deposition may be useful to reduce the manufacturing costs or to use a flexible substrate, for example, a plastic substrate.